MMIX has a "SADD" instruction, which does popcount(x&~y). (You could use this to count trailing zeros with two instructions, each taking only one clock cycle.)

MMIX has a "SADD" instruction, which does popcount(x&~y). (You could use this to count trailing zeros with two instructions, each taking only one clock cycle.) I thought JavaScript ought to have a built-in popcount function for the new integer type, but last I checked, it doesn't have. (It would be faster than writing JavaScript code to emulate it.) (I can think of uses for popcount on arbitrary length integers. Of course this won't work with negative numbers (I don't care what it does if the input is negative, although they should define what it does in that case), but for nonnegative numbers would be good to have.) I have also used the __builtin_popcount function in GNU C. I did not know that it can detect an implementation of popcount and replace it; I have just used the built-in function. I also did not know of all of the uses mentioned in the linked document (but I did know of some other uses).